Graft arteriosclerosis (GA), the major cause of late cardiac allograft failure, is untreatable so that improved clinical outcomes will depend upon prevention. We have proposed that GA is caused by chronic delayed type hypersensitivity in which host T cells recognize non-self antigens presented by graft endothelial cells (ECs) and produce IFN-3, a cytokine that produces GA-like lesions in human artery segments transplanted into immunodeficient mice and that is found in clinical specimens of GA. This project will explore three approaches to reduce IFN-3 production by human memory T cells responding in vivo to transplanted allogeneic human artery segments in mouse hosts or in vitro to cultured allogeneic human ECs. First, we will subject human arterial segments to controlled hypoxia followed by reperfusion in vivo or subject cultured human endothelial cells (ECs) to hypoxia followed by reoxygenation in vitro, characterize the effect on allogeneic T cell responses, and determine if neutralization of specific vascular cell-derived mediators induced by these conditions can reduce IFN-3 production. Second, we will determine if antibodies reactive with EC antigens, especially HLA-A,B,C, alter ECs in a manner that increases allogeneic T cell responses, determine if complement activation is involved, and determine if neutralizing complement or EC-derived mediators induced by antibodies can reverse this effect. Third, we will determine conditions under which ECs induce the development or function of T regulatory cells (i-Tregs) that can reduce IFN-3 production by effector cells, characterize such i-Tregs, and develop strategies to generate such i-Tregs in vivo. In parallel, we will convert effector T cells to i-Tregs by FoxP3 protein transfection. Our hypothesis regarding the interactions of humoral and cellular immunity is novel and our creation of new humanized mouse models and our use of protein transfection to convert T effector cells to i-Treg-like cells are methodologically innovative. Successful completion of these aims may lead to new preventative therapies that target GA.